The present invention relates generally to fasteners and more specifically to two piece fasteners which are adapted to be utilized in securing a broad range of material thicknesses.
In some applications it would be desirable to use a two piece fastener of the type employing a pin having combination locking and breakneck grooves and a tubular member adapted to be swaged thereto and in which any of these grooves is capable of functioning as a breakneck so as to enable a single fastener to be utilized over a broad range of material thicknesses. One problem with such a fastener is providing a structure in which the pin break will occur repeatedly and consistently in a desired one of the combination grooves. Attempts to provide such a structure have generally included a pin having substantially identical combination locking and breakneck grooves. See, for example, U.S. Pat. Nos. 4,208,943, 4,342,529, and 4,347,728 issued to Smith. In these inventions, an axially directed force generated by the swaging of the tubular member into a preselected one of the combination grooves is utilized at a preselected groove which force when combined with pulling force applied by an installation tool will provide a combined tensile force at the selected groove whereby fracture will occur and hence that groove when selected functions as a breakneck. However, because the tubular member is swaged into a plurality of combination grooves which are substantially identical prior to the pin breaking, and because minor uncontrolled differences actually occur in the groove dimensions as a result of manufacturing variations, the pin break may not repeatedly and consistently occur in the desired groove.
In some instances it has been desirable to use multigrip fasteners with installation tools having jaws of a conventional structure. This has necessitated using pins with pull grooves that engage the jaws of the tool which have stress concentration factors which are substantially different than the stress concentration factors for the combination grooves. Because of the difference in shape between the pull grooves and combination grooves, it may be necessary to roll these grooves in separate manufacturing processes or to provide a transition portion located between the pull grooves and combination grooves. This transition portion adds unnecessary material and cost to the pin.
Accordingly, it is an object of this invention to provide a multigrip fastener with a higher degree of installation reliability than those currently available.
It is another object of this invention to minimize the fastener, cost.